Stirring hot plates are widely used in the chemical, medical, food and agricultural technology industries. A stirring hot plate has a stationary base on which the fluid container rests. A magnetic stir bar is inserted into the container, and the magnetic stir bar is coupled by a magnetic field to magnets located beneath the table. Rotating the magnets beneath the table rotates their coupling magnetic fields and causes a corresponding rotation of the magnetic stir bar in the liquid. Simultaneously with the stirring action, the fluid can be heated to a desired temperature.
Often, a user desires to execute successive identical magnetic stirring processes. With known magnetic stirrers, this can be accomplished with two methods. With a first method, when a first process is completed, the stirrer is turned off; the fluid containers exchanged and stirrer restarted. However, with some magnetic stirrers, the stirring speed set point may be lost and have to be reset. With a second method, when a first stirring process is done, the user simply lifts the fluid container off of the stirrer without stopping the stirring motor, stirrer, thereby abruptly decoupling the magnetic stir bar from the magnet. That abrupt decoupling results in the magnetic stir bar clanging around in the beaker. When the second next fluid container is placed on the stirrer, depending on the stirring speed, the magnetic stir bar may not automatically couple; and the stirring speed must be reduced until a magnetic coupling is achieved. Thus, there is a need for a stirrer cycle that permits fluid containers to be quickly unloaded from and loaded onto the stirrer with a minimum of user intervention and unnecessary stirring bar motion.
During operation of a stirring hot plate, the platform on which the container rests is often heated to a temperature that is hot-to-the-touch; and many stirring hot plates provide a visual indicator that is on whenever the temperature of the hot stirring plate exceeds a hot-to-the-touch temperature. When the stirring hot plate is operating, users are normally aware of the potential for the platform to be hot-to-the-touch; and they are more careful. However, after an operating cycle, when the power is turned off and the fluid container removed, users are less likely to be conscious of the platform being hot-to-the-touch and may not see the illuminated hot-to-the-touch indicator. Therefore, there is a further need to provide an improved indication to the user that the platform is hot-to-the-touch.